A joint of this general type has been disclosed in my prior U.S. Pat. Nos. 3,864,786 and 3,477,086. The leaf spring conventionally employed are strips of sheet steel of generally V-shaped configuration with two diverging legs interconnected by a bight portion whose radius of curvature should be as small as possible. Sheet steel having the requisite elasticity, however, is of limited malleability which imposes a certain minimum value upon the ratio between radius of curvature and sheet thickness.